Generally, two types of injury trauma exist, those caused by force and those caused by overuse. Force traumas cause injuries in which an individual receives an acute injury to body tissues. Examples of force traumas include: broken bones, dislocations, muscle bruises, blunt trauma, sprains, and other wounds. Overuse injuries are caused by repetitive overuse of certain body tissues resulting in microscopic tissue injury. Generally, the body is not allowed adequate time to heal because the individual fails to adequately recover from continually repeated movement or prior workouts. As a result, minor injuries are aggravated into more serious injuries. Examples of overuse injuries include: shin splints, tendonitis, carpal tunnel injuries, and stress fractures. Pathology and disease states such as arthritis, lupus, degenerative muscle disorders may also cause or result in injury to tissues and pain.
Injuries are generally classified as acute or chronic. An acute injury is a recent injury that occurred as a result of a traumatic event or action. Acute injuries include: muscle pulls, ligament sprains, fractures, dislocations, contusions and bruises, among other things. Chronic injuries occur as a result of overuse or a long-standing condition. Chronic injuries seen in orthopedics include: overuse syndromes, tendonitis, bursitis and arthritis. Overuse syndromes, also called cumulative trauma disorder (CTD) or repetitive strain injury (RSI), are conditions characterized by chronic irritation to a body part. Many conditions fall within the category of overuse syndromes.
“Tissue” refers to soft tissue, muscle tissue, bone tissue, tendons, ligaments and cartilage among other things. In general, the healing process for traumatized tissue follows a specific physiological sequence. Within the first 24 hours, a series of vascular, cellular and chemical events occur following an initial trauma. Immediately following an injury that is, during the acute phase, blood flow to the injury site increases. Blood vessels, broken during injury, are sometimes not able to contain the blood flow to the injured area. As a result blood spills into the injured area, causing inflammation, or more commonly, swelling, of the area. There are two primary causes of pain in injuries, (1) a nerve ending sending an impulse to the brain and (2) inflammation causing nerve endings to be stretched and send an impulse to the brain.
There are certain factors that impede tissue healing. The nature or the amount of the inflammatory response is determined by the extent of the tissue injury. Edema impedes tissue healing because the increased pressure caused by swelling retards the healing process, causes separation of tissues, inhibits neuromuscular control, produces reflexive neurological changes and impedes nutrition to, and waste removal from, the injured area. Bleeding, or hemorrhage, occurs with even the smallest amount of damage to the capillaries which can add to further inflammation. Additional inflammation adds more pressure and pain to the injured area.
Vascular supply to the area has an effect on healing and also has an effect on the healing process. Injuries to tissues with a poor vascular supply heal poorly and at a slower rate. For example, injuries to tendons and ligaments, in general, heal more slowly because they have low vascular supply. The type of tissue injury can also affects the healing process. In general, mechanically separated, smooth edges heal better and more quickly than jagged edged damaged tissue. Muscle spasms in the injured area may also affect healing as traction on torn tissue prevents approximation of the injured edges of the tissue. Atrophy, the wasting away of muscle tissue, begins immediately with trauma. Oxygen tension relates to the neovascularization of the wound. Optimal saturation with oxygen is required for the return of maximal tensile strength and development. Of course, the health, age and nutrition intake of the individual will also affect the healing capacity of the body to the injury. Acute injuries become chronic injuries when the body ceases to be able to cope with the tissue destruction, edema, and/or continued overuse. Pain and swelling continues at rest and the movement or joint motion remains suboptimal for days to months or more.
A joint is the location at which two or more bones come together within the anatomical structure. Joints allow movement and provide mechanical support. Joints are mainly classified structurally and functionally.
Structural classification is determined by how the bones connect to each other. There are three structural classifications of joints. A fibrous joint is joined by fibrous connective tissue, while a cartilaginous joint is joined by cartilage. Synovial joints are not directly joined.
Functional classification is determined by the degree of movement between the articulating bones and the amount of mobility that they allow. A synarthrosis joint permits little or no mobility. Most synarthrosis joints are fibrous joints, such as those, for example, in the skull. An amphiarthrosis joint permits slight mobility. Most of these joints are cartilaginous joints, for example, vertebrae. A diarthrosis joint permits a variety of movements. All diarthrosis joints are synovial joints. Such joints include the shoulder, hip, elbow and knee. A diarthrosis and a synovial joint are considered equivalent.
Joints can also be classified based on their biomechanical properties. Biomechanically, joints are subdivided into simple, compound and complex. Simple joints have two articulating surfaces, such as the shoulder and the hip. Compound joints such as the radiocarpal, or wrist joint, have 3 or more articulating surfaces. A complex joint such as the knee has 2 or more articulating surfaces and an articular disc or meniscus.
With the foregoing basic understanding of anatomy and physiology, one recognizes that joint and muscle mechanics are interconnected. Bones are required for movement and locomotion, but they are unable to move on their own. They must be moved by the alternate contraction and relaxation of the skeletal muscles. Skeletal muscles (also known as striated, voluntary muscles and skeletal muscle) act on the bones that serve as a system of levers. Voluntary muscles control the movement that you have direct control over. These muscles are responsible for making almost any movement that is required. Voluntary muscles are also found in your face and jaws, so they are used when you smile or frown and when you talk, eat or drink.
Joints are the points at or around which the bones move to create motion. Many bones have ridges and protuberances which provide an area for muscle attachment. Muscles may move the whole body, or part of it, or some material along a tube within it. That is, movement does not depend on movement from only one joint (location). Specific joint stability is not solely dependant on the stability of that specific joint alone. This being said, injuries to one joint affect other joints and musculature and therefore the support and rehabilitation of anatomy, and training for a certain action, often requires rehabilitation and training of other areas of the body, often in conjunction with the perceived injured joint and musculature.
For every muscle or group of muscles that bring about movement of a certain part of the body, there is another muscle, or group of muscles, which bring about an opposite movement. All muscles work in pairs. This is because muscles can contract and relax but cannot push or stretch themselves. Muscles that bring about opposite movements are called antagonistic muscles. As the one muscle contracts, the other relaxes, and vice versa. The antagonistic action allows the smooth coordination of movement possible. When a muscle is stimulated it contracts and becomes shorter and thicker thus moving the bone to which it is attached. When it is relaxed, the muscle becomes longer and thinner. For example, in moving one's arm, when the biceps contracts it flexes the elbow joint. At the same time it also pulls the triceps to make it longer. So the triceps is stretched by the biceps pulling it. When the triceps contracts it extends the arm and at the same time it pulls the biceps and makes it longer. So these two muscle groups work together, antagonistically. Movement is brought about by muscles doing work by pulling as they contract. No work is done by a muscle pushing as it elongates.
The functional element of striated muscle is the muscle fiber, which has many fine threads or myofibrils running throughout its length. After nervous stimulation, electrical changes in the membrane surrounding each myofibril cause the release of calcium ions which results in muscle shortening. Oxygen is carried to muscles by the blood, which runs in a plexus of fine capillaries in between the fibers. Waste products such as carbon dioxide and lactic acid are carried away in the blood.
The nerve supply to a striated muscle usually enters along with the blood vessels. The nerve to a muscle is mixed, that is it contains both motor fibers which convey impulses from the spinal cord to the muscle and sensory fibers which relay information back to the spinal cord. The motor fibers branch within the muscle, and one nerve cell supplies several muscle fibers distributed throughout the muscle. Each muscle fiber receives only one terminal branch of a nerve fiber at the neuromuscular junction.
The signal is passed between the two cell membranes, that of the nerve fiber (called the pre-synaptic membrane) and that of the muscle cell (called the post-synaptic membrane). A wave of depolarization (movements of sodium and potassium ions) along the fiber releases calcium ions and initiates the process of contraction.
A sensory receptor is a part of a sensory neuron or cell that receives information from the world and relates it to the nervous system. There are several different types of sensory neurons within the body. For example, Pacinian corpuscles in the skin are the deep pressure receptors. Some outside force has to have a way to act on the sensory nerve. In the case of the Pacinian corpuscle, a very forceful pressing on the skin activates it. Mechanoreceptors respond to mechanical stress or mechanical strain. Muscle spindles contain mechanoreceptors that detect stretch in muscles. Nociceptors respond to damage to body tissues leading to pain perception. Thermoreceptors respond to temperature, either heat, cold or both. Cutaneous receptors are sensory receptors found in the dermis or epidermis. Proprioceptors provide the sense of position.
Within and around a joint are many structures required to allow function of that structure. There are many muscles and tendons, which insert or originate on the distal end of the femur or proximal end of the tibia and fibula and cover and support the patella. The femur, tibia and patella are the bones that create the knee joint. There are ligaments that hold bone to bone and cartilage is at the distal and proximal ends of the bone to cushion areas of bone to withstand force and to protect the bone from wear and tear. A bursa is a small fluid filled sac or saclike cavity situated in places in tissues where friction would otherwise occur. Bursae function to facilitate the gliding of skin, muscles or tendons over bony or ligamentous surfaces. They are numerous and are found throughout the body; the most important are located at the shoulder, elbow, knee and hip. Inflammation of a bursa is known as bursitis. Synovium is the smooth lining of a joint. A flexible joint is lined by a synovial membrane. Synovium produces synovial fluid (illustration), a clear substance that lubricates and nourishes the cartilage and bones inside the joint capsule. Injury to any of these structures (muscle, tendon, ligament, cartilage, meniscus, bursa or synovium) can result in pain. There are two menisci in your knee. The medial meniscus is on the inside of the knee while the lateral meniscus is on the outside of the knee. Each meniscus rests between the thigh bone (femur) and shin bone (tibia). The menisci are made of tough cartilage and conform to the surfaces of the bones upon which they rest. These menisci function to distribute the body weight across the knee joint. If the meniscus was not present, the body weight would be unevenly applied to the bones in the legs (femur and tibia).
Relative strength differences between ligament and bone can predict the location of injury within the joint. In pediatric patients, the ligament is generally strongest at the growth plate or the bone is weakest at the growth plate. When there is stress on the joint, injury is likely to occur at the growthplate. With an adult, bone is normally stronger than the structure of the ligament. As a result, in an adult, ligaments rupture first. In geriatrics patients, the ligament is stronger than the bone. As a result, frequently, the bone will fracture first.
Sprains occur when there is a tear to a ligament. Grade I sprains result from stretching of the ligament or a minor tear of the ligament. There is no laxity of the ligament. Grade II sprains are a result of an incomplete tear. Laxity of the ligament is evident and there is usually swelling associated with the injury. A Grade III sprain is characterized by a complete tear of the ligament. There is increased laxity of the ligament with swelling (edema). The individual is definitely experiencing pain.
The most common cause of joint pain is overuse and/or repetitive motion. Certain types of athletic activities employ repetitive motion. Other repetitive motion pain and injury occurs through simple use of a joint over time. Overuse injuries are also frequently work-related injuries associated with continued repetitive motion such as typing, working with tools and other simple repetitive motions.
Overuse injuries are caused in two basic ways. In the first scenario, the movement is inconsistent with the anatomy used to make the movement. Alternatively, repetitive motion can cause muscle fatigue to exhaustion and stress is on the insertion or origin of the muscular tendon. Repetitive rubbing of the tendon thru a boney canal causes inflammation and therefore, pain thru that area.
Pain is the patient's first warning of an injury. If pain continues, the area will continue to experience damage and swelling will increase. Swelling results in pressure and damage results in bleeding (hemorrhage) which also results in pressure. Pressure and structural damage trigger pain receptors within the tissue.
The physical response to inflammation is pain to the individual. Continued movement of the painful area often results in further injury. Once tissue is injured, it takes longer to heal and may require surgical intervention.
Age can define what kind of damage occurs at a joint. The young tend to receive trauma, fractures, or ligamentous and meniscal injuries. The middle age to older individuals are often struck by arthritis. The most common form of arthritis is osteoarthritis or degenerative joint disease. Arthritis can occur following trauma or an infection of the joint. Arthritis may occur from aging alone. Abnormal anatomy may contribute to early development of osteoarthritis. It is the leading cause of disability in people over the age of 55.
For the person experiencing the pain, it is sometimes difficult to identify the origin of the pain. For example, when a patient has a “sore knee” it can be the whole knee that is in pain. Diagnosis is simpler during the acute phase of an injury as the patient may have been more likely to pinpoint the location of specific pain.
Early identification of the injury frequently narrows down the offending movements sooner and could lead to injury prevention. However, most people, particularly athletes, continue workout and therefore continue to subject the injured area to the offending motion until the pain is more global and affects more of the joint. Unfortunately, by that time other muscle groups are involved and it is more difficult to understand where and what caused the injury.